Analyte pre-concentrator for gas chromatography

ABSTRACT

An analyte pre-concentrator for gas chromatography is disclosed generally comprising a tube having a restricted outlet and packed with an adsorbent, wherein the tube serves as the liner of a chromatographic injector, as an adsorbent trap coupled to a chromatographic column, and/or as an adsorbent trap coupled to a headspace sampler. Preferably, a heating device allows the tube to be heated. In a preferred embodiment, the analyte pre-concentrator further comprises a column isolating accessory so that a chromatographic column can be temporarily isolated from substances flowing through the tube.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation of U.S. patent application Ser. No. 10/625,259,filed Jul. 22, 2003 now U.S. Pat. No. 6,814,785, which is a continuationof U.S. patent application Ser. No. 10/202,147, filed Jul. 24, 2002, nowU.S. Pat. No. 6,652,625.

FIELD OF THE INVENTION

The present invention relates to a method and apparatus forpre-concentrating analytes and removing moisture in a sample. Morespecifically, the invention relates to an adsorbent trap for use withchromatographic columns, chromatographic injectors, and headspacesamplers.

BACKGROUND OF THE INVENTION

Chromatography is essentially a physical method of separation in whichconstituents of a test sample in a carrier gas or liquid are adsorbed orabsorbed and then desorbed by a stationary phase material in a column. Apulse of the sample is introduced into a steady flow of carrier gas. Atthe end of the column, the individual components are more or lessseparated in time. Detection of the gas provides a time-scaled patternthat, by calibration or comparison with known samples, indicates theconstituents of the test sample. An example of the process by which thisoccurs is described in U.S. Pat. No. 5,545,252 to Hinshaw et al.

The value of using a separate, heated device for receiving the sampleand subsequently introducing it into the column has long beenrecognized. One such device is disclosed in U.S. Pat. No. 4,038,053 toGolay, which describes using a chromatographic injector for receivingthe sample, heating it, and subsequently injecting it into achromatographic column. Such a device is desired because higher sampleequilibrium temperatures can result in much larger chromatographicpeaks. A disadvantage of such devices, however, is that such temperatureincreases may also increase the concentration of other material thatdetrimentally affects the sensitivity of the system, such as water.

To remedy this problem, numerous assemblies have been suggested topre-concentrate analytes in a sample and remove moisture therefrom priorto introducing the sample into a chromatographic column. For example,U.S. Pat. No. 5,612,225 to Beccanti et al., U.S. Pat. No. 4,245,494 toLegendre et al., and U.S. Pat. No. 2,813,010 to Hutchins disclose ameans for removing water from a sample prior to introducing the sampleinto a chromatographic column by first passing the sample through ananhydrous substance, which absorbs the water. However, because theanhydrous substance absorbs the water, rather than adsorbing the analyteand allowing the water to be purged from the system, repeated use of theanhydrous substance is likely to be limited and require frequentreplacement.

Several assemblies have been suggested which utilize an adsorbent trap,which adsorbs the analytes while allowing water to pass through. Forexample, U.S. Pat. No. 6,223,584 to Mustacich et al. discloses the useof an adsorbent trap in a pre-concentrator assembly forpre-concentrating analytes in a sample prior to introducing the sampleinto a chromatographic column, which device comprises a tube containingan adsorbent material. However, a disadvantage of this arrangement isthe dead volume that exists between the adsorbent bed and thechromatographic column, which is undesirable because, at typical columnflow rates, excessive peak broadening results.

U.S. Pat. No. 5,814,128 to Jiang et al. discloses the use of anadsorbent trap in conjunction with a separate water management device,which device removes water from a sample prior to entry into achromatographic column via the swirling motion caused by a threaded (orother non-smooth geometrically shaped) bore in the device. Similarly,U.S. Pat. No. 4,293,316 to Block discloses the use of an adsorbent trapin conjunction with a membrane separator device, which device removeswater from a sample prior to entry into a gas analyzer. However, ratherthan optimizing the utility of the adsorbent trap itself as a means foranalyte pre-concentration and moisture elimination, these assemblieseach require a separate device in addition to the trap, which not onlycreates additional manufacture and maintenance costs, but also does notsolve the aforementioned problem of excessive volume between theadsorbent bed and the chromatographic column.

One means of introducing a sample containing an analyte into achromatographic column is known as “headspace sampling.” In conventionalheadspace sampling, sample material is sealed in a vial and subjected toconstant temperature conditions for a specified time. Analyteconcentrations in the vial gas phase should reach equilibrium with theliquid and/or solid phases during this thermostatting time. The vial issubsequently pressurized with carrier gas to a level greater than the“natural” internal pressure resulting from thermostatting andequilibration. Then the pressurized vial is connected to thechromatographic column in such a way as to allow for the transfer of aportion of the vial gas phase into the column for a short period oftime. Such a system is disclosed in U.S. Pat. No. 5,711,786 to Hinshaw,which describes using a chromatographic injector between the vial andthe chromatographic column. However, the use of such devices presentlyknown in the art, including chromatographic injectors, for headspaceapplications results in the same disadvantages previously mentioned forintroducing samples into chromatographic columns generally.

What is desired, therefore, is a method and apparatus forpre-concentrating analytes and eliminating moisture in a sample prior tointroducing the sample into a chromatographic column. What is furtherdesired is a method and apparatus for pre-concentrating analytes andeliminating moisture in a sample in a chromatographic injector. What isalso desired is a method and apparatus for pre-concentrating analytesand eliminating moisture in a sample in connection with a headspacesampler.

SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to provide an analytepre-concentrator for gas chromatography that permits temperatureincreases without detrimentally affecting the sensitivity of thechromatographic system.

It is a further object of the present invention to provide an analytepre-concentrator for gas chromatography that provides a moisture trappermitting moisture to be purged from the chromatographic system so thatthe trap may be used for multiple injections.

It is yet another object of the present invention to provide an analytepre-concentrator for gas chromatography that provides a moisture trapresulting in little or no dead volume between the trap and achromatographic column, thereby decreasing excessive peak broadening.

It is still another object of the present invention to provide ananalyte pre-concentrator for gas chromatography that provides a moisturetrap without the addition of a separate device, thereby decreasingmanufacturing and maintenance costs.

It is still another object of the present invention to provide a methodfor pre-concentrating analytes in a gas chromatographic system thatachieves the objects listed above.

To overcome the deficiencies of the prior art and to achieve at leastsome of the objects and advantages listed, the invention comprises achromatographic injector, a liner located inside the injector, the linerhaving an inlet and an outlet, wherein the inner diameter of the outletis smaller than the inner diameter of the inlet, and an adsorbentlocated inside the liner. Preferably, the injector is temperaturecontrollable.

In another embodiment, the invention comprises a tube having an inletand an outlet, wherein the inner diameter of the outlet is smaller thanthe inner diameter of the inlet, an adsorbent located inside the tube,and a gas chromatographic column coupled to the tube. Preferably, theinvention further comprises a heating device for heating the tube.

In another embodiment, the invention comprises a headspace sampler, atube coupled to the headspace sampler, the tube having an inlet and anoutlet, wherein the inner diameter of the outlet is smaller than theinner diameter of the inlet, and an adsorbent located inside the tube.Preferably, the invention further comprises a heating device for heatingthe tube.

In a preferred embodiment, the invention further comprises a columnisolating accessory, with which a chromatographic column can betemporarily isolated from the tube or liner.

The invention also relates to a method comprising the steps of settingthe pressures of a main carrier gas inlet and an auxiliary carrier gasinlet such that a column is isolated from substances flowing through atube, introducing a sample mixture into the tube, such that the mixturepasses through an adsorbent, which adsorbs the analytes, and is ventedfrom the chromatographic system, introducing additional carrier gas intothe tube, such that moisture is dry purged from the adsorbent, settingthe pressures of the main carrier gas inlet and the auxiliary carriergas inlet such that the column is no longer isolated from substancesflowing through the tube, and heating the tube, such that the analytesadsorbed by the adsorbent are desorbed into the column.

The invention and its particular features will become more apparent fromthe following detailed description when considered with reference to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a gas chromatographic sampling systemincluding a headspace sampler and a gas chromatograph in accordance withthe invention.

FIG. 2 is an isometric view of a chromatographic injector and a columnisolating accessory connected to the bottom of the injector for use withthe chromatographic sampling system of FIG. 1.

FIG. 3 is an exposed side view of the chromatographic injector andcolumn isolating accessory of FIG. 2.

FIG. 4 is a perspective view of a tube used as a liner insidechromatographic injectors known in the prior art.

FIG. 5 is a perspective view of an empty tube used as a liner inside thechromatographic injector of FIG. 3.

FIG. 6 is a side view of the tube of FIG. 5 containing an adsorbent.

FIG. 7 is an exposed side view of the gas chromatographic system of FIG.1 during the vial pressurization stage.

FIG. 8 is an exposed side view of the gas chromatographic system of FIG.1 during the analyte adsorption stage.

FIG. 9 is an exposed side view of the gas chromatographic system of FIG.1 during the dry purge stage.

FIG. 10 is an exposed side view of the gas chromatographic system ofFIG. 1 during the analyte desorption stage.

FIG. 11 is an exposed side view of a gas chromatographic system of FIG.1 during the cleanup stage.

DETAILED DESCRIPTION OF THE INVENTION

The basic components of one embodiment of a gas chromatographic samplingsystem 10 in accordance with the invention are illustrated in FIG. 1. Asused in this description, the terms “top,” “bottom,” “upper,” and“lower” refer to the objects referenced when in the orientationillustrated in the drawings, which orientation is not necessary forachieving the objects of the invention.

In the embodiment depicted in FIG. 1, a headspace sampler 12 holds aplurality of vials 14 that contain the sample to be analyzed. Theheadspace sampler 12 is connected to a gas chromatograph 16 via atransfer line 18. The basic components of the gas chromatograph are aninjector 20, a chromatographic column 80, and a detector (not shown).

The basic components of one embodiment of the injector 20, an example ofwhich is the Programmed-Temperature Split/Splitless Inlet System (PSS)Injector manufactured by PerkinElmer Instruments LLC, are illustrated inFIGS. 2 through 3. A metal sleeve 22 creates a chamber 24 in which aremovable tube 26 that serves as the “liner” of the injector 20 isinserted. The sleeve 22 is located inside a heater block 28, which isgoverned by a heating element 30, for heating the chamber 24, includingthe liner 26. The heater block 28 is provided with cooling fins 32, anda fan 34 may be coupled to a housing 36 for subsequently cooling thechamber 24 and liner 26.

Referring to FIGS. 5 through 6, the main features and components of theliner 26 are illustrated. Preferably, the liner 26 is glass. The liner26 has an inlet 70 located at its top and an outlet 72 located at itsbottom. The outlet 72 is restricted, such that the bottom of the liner26 has an inner diameter smaller than that of the top. A glass disk 74rests at the top of the restricted bottom of the liner. Above the disk74, the liner is packed with an adsorbent material 76 capable ofadsorbing analytes. Preferably, the adsorbent 76 is hydrophobic. Onesuch adsorbent is graphitized carbon black, such as Carbopack B,manufactured by Supelco. The restricted outlet 72 serves the dualpurpose of firmly retaining the adsorbent 76 and significantly reducingthe dead volume between the adsorbent 76 and the column 80. Preferably,a glass/quartz wool plug 78 is located above the adsorbent 76 both tofacilitate mixing of the sample vapor and the carrier gas and to serveas a surface on which nonvolatile residues from the sample vapor aredeposited, thereby permitting easier cleaning of the liner 26. As shownin FIG. 6, the column 80 may be inserted directly into the bottom of theliner 26.

Referring again to FIGS. 2 through 3, a threaded collar 40 secures aseptum assembly 42 to the housing 36 at the top of the metal sleeve 22.A septum cap 44 secures a septum 45 to the top of the septum assembly42, through which septum a microsyringe 82 may inject the sample.

The septum assembly 42 has a main carrier gas inlet 46, the pressure ofwhich can be regulated, which is located above, and separated from thechamber 24 by, an internal seal 48, such as an o-ring. Additionally,septum assembly 42 has a septum purge outlet 50. The septum assemblymechanically defines the path of the septum purge flow to prevent crosscontamination with the sample flow path.

Preferably, a “split” vent 52, for splitting the gas mixture, is locatedbelow the internal seal 48 and is in fluid communication with thechamber 24.

Preferably, a column isolating accessory 60, such as the PreVent™ Systemmanufactured by PerkinElmer Instruments, LLC, is interposed between thebottom of the injector 20 and the chromatographic column 80. Theaccessory 60 has an auxiliary carrier gas inlet 62, the pressure ofwhich can be regulated. Additionally, the accessory may have arestrictor tubing (not shown) which is inserted into the bottom of theliner 26 and the top of the column 80 when the accessory is coupled tothe bottom of the injector 20.

Operation of the above described gas chromatographic system 10 isillustrated stepwise in FIGS. 7–11. Beginning in FIG. 7, a samplingneedle 82 descends into a vial 14. A headspace sampler carrier gas inlet84 is open to allow carrier gas to pressurize the vial 14 (indicated byarrows A). The main carrier gas inlet 46 is open and set at a pressureappropriate to introduce carrier gas into the injector 20 (indicated byarrows B), and the auxiliary carrier gas inlet 62 is open and set at aslightly lower pressure than the main carrier gas inlet 46 in order tointroduce carrier gas into the injector 20 to isolate thechromatographic column 80 from the injector 20 (indicated by arrows C).

Referring to FIG. 8, the headspace sampler carrier gas inlet 84 isclosed, and headspace vapor elutes from the vial 14, down the transferline 18, through the septum 45, into the injector 20, and into the liner26 (indicated by arrows D). Carrier gas entering the injector from themain carrier gas inlet 46 mixes with the sample vapor, which mixing isfurther facilitated by the glass/quartz wool plug 78, and helps to carrythe sample vapor through the adsorbent 76 and out the restricted outlet72 (indicated by arrows E), at which point it mixes with carrier gasentering the injector 20 from auxiliary carrier gas inlet 62 (indicatedby arrows C), and out the split vent 52 (indicated by arrows Z).

Referring to FIG. 9, the sampling needle 82 is removed from the vial 14and the headspace sampler carrier gas inlet 84 is re-opened. The carriergas supplied by the inlet 84 and the main carrier gas inlet 46 flowthrough the adsorbent 76 and dry purge the water therefrom (indicated byarrows F). Because the auxiliary carrier gas inlet 62 is still set at apressure appropriate to isolate the chromatographic column 80 (indicatedby arrows C), the water and other unwanted substances that exit therestricted outlet 72 are carried along the outside of the liner 26 andout the split vent 52 (indicated by arrows G). A small additional flowpasses over the exposed surface of the septum 45, sweeping volatilecontaminants away from the main carrier gas flow, and passes through theseptum purge outlet 50 (indicated by arrows H).

Referring to FIG. 10, after the water has been removed, the split vent52 is closed and the pressure of the main carrier gas inlet 46 isincreased to permit flow into the column 80 (indicated by arrows I). Thechamber 24, including the liner 26, is heated with the heater block 28so that the analytes adsorbed by the adsorbent 76 are desorbed into thecolumn 80 (indicated by arrows J).

Referring to FIG. 11, after the analytes have been transferred to thecolumn 80, the pressure of the main carrier gas inlet 46 is decreased toagain allow the carrier gas introduced into the injector 20 by theauxiliary carrier gas inlet 62 to isolate the column 80 from theinjector 20 (indicated by arrows C). The liner 26 is further heated todrive any remaining unwanted less volatile residue off of the adsorbent76 and out through the split vent 52 (indicated by arrows K).

It should be understood that the foregoing is illustrative and notlimiting, and that obvious modifications may be made by those skilled inthe art without departing from the spirit of the invention. Accordingly,reference should be made primarily to the accompanying claims, ratherthan the foregoing specification, to determine the scope of theinvention.

1. An analyte pre-concentrator for use with a chromatographic column,comprising: an adsorbent housing; an adsorbent disposed in said housing;wherein the inner wall of the upper portion of said housing partiallyencloses an upper chamber in which said adsorbent is disposed; whereinthe inner wall of the lower portion of said housing partially encloses alower chamber in which a portion of the chromatographic column isdisposed; wherein the diameter of the lower chamber is smaller than thediameter of the upper chamber.
 2. The analyte pre-concentrator of claim1, wherein said adsorbent housing comprises a tube.
 3. The analytepre-concentrator of claim 1, wherein said adsorbent is hydrophobic. 4.The analyte pre-concentrator of claim 3, wherein said adsorbentcomprises graphitized carbon black.
 5. The analyte pre-concentrator ofclaim 1, further comprising a headspace sampler in fluid communicationwith the upper chamber of said adsorbent housing.
 6. The analytepre-concentrator of claim 1, further comprising a heating elementdisposed adjacent said adsorbent housing for increasing the temperatureof said housing.
 7. The analyte pre-concentrator of claim 1, furthercomprising: a first fluid pathway in which a sample mixture containinganalytes mixes with carrier gas, flows through said adsorbent, whichadsorbs the analytes, and is vented from said housing; and a secondfluid pathway in which the analytes adsorbed by said adsorbent aredesorbed into the column.
 8. A system for pre-concentrating analytes,comprising: a headspace sampler; an adsorbent housing in fluidcommunication with said headspace sampler, said housing having an inletand an outlet, wherein the inner diameter of the outlet is smaller thanthe inner diameter of the inlet; an adsorbent disposed in said housing;a chromatographic column in fluid communication with said adsorbenthousing.
 9. The system of claim 8, wherein said adsorbent housingcomprises a tube.
 10. The system of claim 8, wherein said adsorbent ishydrophobic.
 11. The system of claim 10, wherein said adsorbentcomprises graphitized carbon black.
 12. The system of claim 8, furthercomprising a heating element disposed adjacent said adsorbent housingfor increasing the temperature of said housing.
 13. The system of claim8, further comprising: a first fluid pathway in which a sample mixturecontaining analytes mixes with carrier gas, flows through saidadsorbent, which adsorbs the analytes, and is vented from said housing;and a second fluid pathway in which the analytes adsorbed by saidadsorbent are desorbed into the column.
 14. A system forpre-concentrating analytes, comprising: a container for holding a samplecontaining the analytes; a sampling device for receiving the analytesfrom said container; an adsorbent housing in fluid communication withsaid sampling device, said housing having an inlet and an outlet,wherein the inner diameter of the outlet is smaller than the innerdiameter of the inlet; an adsorbent disposed in said housing; achromatographic column in fluid communication with said adsorbenthousing.
 15. The system of claim 14, wherein said adsorbent housingcomprises a tube.
 16. The system of claim 14, wherein said adsorbent ishydrophobic.
 17. The system of claim 16, wherein said adsorbentcomprises graphitized carbon black.
 18. The system of claim 14, furthercomprising a heating element disposed adjacent said adsorbent housingfor increasing the temperature of said housing.
 19. The system of claim14, further comprising: a first fluid pathway in which a sample mixturecontaining analytes mixes with carrier gas, flows through saidadsorbent, which adsorbs the analytes, and is vented from said housing;and a second fluid pathway in which the analytes adsorbed by saidadsorbent are desorbed into the column.